Loadstones and Earths
Loadstones and Earths
Jöns Jacob Berzelius (1779–1848), discoverer of the elements selenium, thorium, cerium, and silicon and deviser of the chemical symbols we use today, was one of the last in a long list of Swedish mineralogists and chemists active during the eighteenth century. Berzelius himself regarded one of his predecessors, Axel Fredrik Cronstedt (1722–65), as the founder of chemical mineralogy. We met Cronstedt in Chapter 2 as the discoverer of the element nickel, isolated from the ore kupfernickel. But another of Cronstedt’s achievements was perhaps of even greater significance: his development of a classification of minerals based not on their physical appearances, as had been common up to this time, but on their chemical compositions. He first published his scheme anonymously in Swedish in 1758, but it was later translated into English as An Essay towards a System of Mineralogy. Cronstedt recognized four general classes of minerals: earths, bitumens, salts, and metals. As their name suggests, the bitumens were flammable substances that might dissolve in oil but not in water. The main difference between the salts and the earths was that the former, which included the ‘alcaline mineral salt’ natron, could be dissolved in water and recrystallized from it. The earths he defined as ‘those substances which are not ductile, are mostly indissoluble in water or oil, and preserve their constitution in a strong heat’. Cronstedt initially recognized nine different classes of earth. By the time of Torbern Bergman (1735–84), these had been reduced to five which ‘cannot be derived from each other or from anything simpler’. Lavoisier and his collaborators included these five in their great work on nomenclature even though they suspected that, like soda and potash, they were most likely not simple substances, but species that contained new metals. In the 1788 English translation of the nomenclature these were called silice, alumina, barytes, lime, and magnesia. The first two eventually, in the early nineteenth century, yielded the elements silicon and aluminium. The word ‘silicon’ derives from the Latin ‘silex’ (meaning ‘flint’—a form of silicon dioxide), with the ending ‘-on’ reflecting its resemblance to the other non-metals carbon and boron.
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